The Compressed Gas Association (CGA) splits compressed gases into two primary categories depending on their physical state in containers under pressures and temperatures, and in their range of boiling points:
nonliquefied gases and liquefied gases. When nonliquefied gases, which are those that are gaseous at ordinary ambient temperatures regardless of pressure applied, are cooled to temperatures below their boiling points, they become liquefied. At these low temperatures, they are referred to as cryogenic liquids. Common examples of cryogenic liquid supplied by Butler Gas Products are oxygen and nitrogen.
Because the temperature difference between the product and the surrounding environment is substantial, keeping the surrounding heat from the product requires special equipment to store and handle cryogenic liquids. A liquid cylinder, commonly called a Liquid Dewar, is constructed like a vacuum bottle; it is designed to keep heat away from the liquid that is contained in the inner vessel. Liquid cylinders operate at pressures up to 350 psig and have capacities between 80 and 450 liters. Product may be withdrawn as a gas by passing liquid through an internal vaporizer or as a liquid under its own vapor pressure.
Cryogenic liquid containers are equipped with pressure relief devices to control internal pressure. Under normal conditions, these containers will periodically vent product (a loud hissing noise); never plug, remove, or tamper with any pressure relief device. Because venting is an intentional design aspect of the container, always store and use liquid cylinders in an open space with adequate ventilation. To move, use a cart designed to handle liquid cylinders. Never allow any unprotected part of the body to come in contact with un-insulated pipes or equipment that contains cryogenic product. Face shields and cryogenic gloves are strongly encouraged. For more safety information, always refer to the product label and SDS.